diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index 234445829..b951eaa9a 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -14,7 +14,7 @@ jobs:
 
   unit-tests:
     name: Unit tests
-    uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
+    uses: apple/swift-nio/.github/workflows/unit_tests.yml@matrix_custom_env_vars # testing
     with:
       linux_5_10_arguments_override: "--explicit-target-dependency-import-check error"
       linux_6_0_arguments_override: "--explicit-target-dependency-import-check error"